Endoscopic Retrograde Cholangiopancreatography (ERCP) is associated with a 5% risk of acute pancreatitis. This investigation will measure the changes in circulating pancreatic enzymes and their inhibitors before and after ERCP. The hope is to demonstrate alterations in proteases:protease inhibitor balance which may predispose to ERCP-induced pancreatitis. This may shed new light on the pathogenesis of pancreatitis.